1. Field of the Invention
The present invention relates to a building board having an anti-algal and antifungal function.
2. Description of the Prior Art
Hitherto, surfaces of external wall materials used for the external walls of buildings such as housings have been coated to protect habitants from weather, light and heat. However, it is not possible to avoid deterioration or inconvenient phenomena such as discoloration, chalking, staining, biotic contamination or the like on the surfaces of external wall materials with aging. Recently, on the other hand, the weather-resistant ability of paints has been considerably improved, and spoil of beauty by the biotic contamination with algae or fungi rather than inconvenience caused by discoloration or chalking has become a serious problem. Such biotic contamination does not occur on the whole surfaces of external wall materials but does predominantly on only a part the wall material (mainly on the northern surface) which does not get sun and is high in temperature and humidity, and thus is humid and suitable for growth of algae and fungi.
Hitherto, biotic contamination occurred on a part of external wall materials has to be dealt with recoating on a large-scale or with washing. Specifically, when the part having biotic contamination is washed, a dilute solution of anti-algal agent or antifungal agent has been sprayed to delay reoccurrence of the biotic contamination. However, such agent is merely temporarily retained, and after washing away of the agent by rain, anti-algal and antifungal effects could not be expected. In addition, the kinds of algae and fungi amount to several hundreds and the kinds of algae and fungi that generate in housings amount to twenty to thirty. Thus, there has not been an agent which is effective for all kinds of algae and fungi. Accordingly, many kinds of agents had to be used, which was not economical. In addition, external wall materials are subjected to dust, weather and ultraviolet rays to result in the staining of the surfaces thereof, and the extraneous matter of this stain resulted in generation of algae and fungi.
Meanwhile, a method for providing an anti-algal effect includes a method of adding an anti-algal agent in a paint (for example, JP 9-235491 A), and a method for providing stain-proofing effect to external wall materials includes a method of applying a paint which comprises silica fine particles, alumina fine particles and/or aluminum magnesium complex oxide fine particles to the surface thereof for the purpose of making the surface hydrophilic (for example, JP 2002-338943 A).